1. Field of the Invention
The present invention relates to deposition masks used for forming hole-transport layers, light-emitting layers and the like for devices such as electroluminescent display units, methods for manufacturing such masks, electroluminescent display units, methods for manufacturing such units, and electronic apparatuses including the electroluminescent display units. The present invention particularly relates to a deposition mask principally used to manufacture an organic electroluminescent display unit (hereinafter referred to as an organic EL display unit) and the like.
2. Description of the Related Arts
Known organic EL display units are usually manufactured by vacuum deposition of organic compounds using a vacuum deposition apparatus in a resistance-heating evaporation system. In particular, for full-color organic EL display units, fine light emitting elements for emitting RGB (red, green, and blue) light must be precisely fabricated. Therefore, such units are manufactured by a mask evaporation process in which organic compounds that are different from each other depending on RGB pixels are selectively deposited on desired regions using metal masks and the like. In order to manufacture full-color organic EL display units with high definition, fine deposition masks must be used. Since such deposition masks must be thin and fine, the masks are conventionally prepared by an electroforming process.
As the definition of the organic EL display units has been enhanced, misalignment due to heat has become serious because known metal masks have a thermal expansion coefficient that is greatly different from that of a deposition substrate treated by a vapor deposition process, made of glass or the like. Especially in the case of using a large-sized deposition substrate treated by a vapor deposition process in order to increase the number of elements obtained from the deposition substrate, the misalignment due to heat is outstandingly caused.
In order to solve that problem, a deposition mask is prepared using a silicon wafer having a thermal expansion coefficient smaller than that of glass.
In order to manufacture a plurality of organic EL display units from a single large-sized deposition substrate, there is a known deposition mask having a configuration that a plurality of second substrates (mask chips), each of which is used for manufacturing one organic EL display unit and formed of a silicon substrate, are joined to a first substrate (a mask support) made of borosilicate glass having apertures. The reason to employ such a configuration is as follows: since an available silicon wafer is disk-shaped having a diameter of about 300 mm at the most, a deposition mask fit for a large-sized deposition substrate cannot be manufactured using such an wafer. Since the first substrate is made of borosilicate glass having a thermal expansion coefficient close to that of silicon, the flexure of the deposition mask is reduced.
In the known deposition mask, when the second substrates consisting of silicon substrates are joined to the first substrate made of borosilicate glass, each of the second substrates must be aligned with the first substrate one by one after one second substrate is joined to the first substrate, and high processing accuracy is necessary; hence, there is a problem in that an increase in the time taken for the process causes an increase in cost.
Since the second substrates have openings according to a pixel pattern, there is a problem in that incorrect pixel pattern is formed if the second substrates are misaligned with the first substrate when they are joined to each other.